For our last trip, we started in IOA and then made our way via Hogwarts Express to USO around 3 pm. This gave us plenty of time to get into our preferred Stay and Scream holding line. Between that strategy and
HHN EP's we made good time around to all the houses, got to see the show and do some rides without having to push too hard that night.
Having said that, we had the luxury of 3 day park to park tickets and the day prior we had a single day of EP's, hit the parks at rope drop and went hard to ride everything we wanted using the EP on that day - I allocated the other two day's EP budget to our HHN EP because I'm too tight to spring for both

LOL!
Mind you, if you aren't doing HHN, it's probably wiser to start in that park and then hop to IOA as suggested above.
HTH
Edit: for context, we did HHN on 31st Oct and were in the parks the day prior and post as well... Crowds were fairly manageable, however, I don't regret the EP for the first day in the parks. - we aren't big 'line' people.